The present invention relates to a technology effective in an application to signal message converting control of a switching equipment for attaining a relay between a narrowband ISDN (N-ISDN) network and a broadband ISDN (B-ISDN).
With a progress and a wide-spread of a technology of an asynchronous transfer mode communication system in recent years, a relay network based on a conventional time division multiplexing (TDM) system has increasingly shifted to a relay network using an ATM line. With this shift, there were made a variety of proposals of a relaying system (disclosed in e.g., Japanese Patent Laid-Open No. 6-232911 etc) from the N-ISDN to the B-ISDN. It is, however, indispensable that communication services (such as, e.g., providing a connection to a priority class terminal) provided in the conventional N-ISDN be also actualized in the B-ISDN.
A notifying method of communication service information between the B-ISDN and the N-ISDN in the prior art, will be explained with reference to the drawings.
As shown in FIG. 2, a permanent virtual channel (PVC) is set as a communication connection between N-ISDN switching equipments (202a, 202b) preset as terminals of B-ISDN switching equipments (201a, 201c) in order to transmit and receive an N-ISDN signal message (information for implementing the communication service) in the B-ISDN. Then, when an N-ISDN call occurs, call setting information is transmitted by use of a present PVC from the call-out N-ISDN switching equipment (202a), and communication service information such as priority class terminal information etc is set therein, whereby the N-ISDN switching equipment (202b) becoming a last call-in station is notified of the priority class terminal information.
On the other hand, for receiving the priority communication services prescribed in the B-ISDN, a quality of service (QOS) must be designated when setting the PVC. For this purpose, as shown in FIG. 3, it is required that the PVC exhibiting a high QOS be previously connected to the call-out from the priority class terminal accommodated in the call-out N-ISDN switching equipment (202a) in order to have the B-ISDN priority communication service received. Then, in the B-ISDN, if the call from the terminal connected to the N-ISDN switching equipment (202a) is recognized as a call transmitted from the priority class terminal, a priority connection in the B-ISDN is actualized by use of the previously-connected PVC.
According to the prior art, however, the PVC in the B-ISDN transmits and receives a cell when set as shown in FIG. 3, and hence there arises a problem in which a band in the B-ISDN is used with a futility even when any call does not occur from the N-ISDN switching equipment (202a).
To obviate the problem described above, it can be considered that the N-ISDN signal message is transmitted and received by use of an SVC connection. In this case, an ITU-T (Q.2931) and an ATM forum (UNI4.0) give such a advise that the last call-in N-ISDN switching equipment be notified of intrinsic information such as the priority class terminal information etc by use of an extended information field defined in the B-ISDN signal message.
Note that the QOS of SETUP is provided with 5-stage classes, a and "class 1" is designated as a contrivance for designating communication priority control in the B-ISDN relay network in the case of the ATM forum (UNI4.0), "class 1" is able to receive the priority control service of an ATM layer more preferentially than other classes (e.g., classes 2, 3, 4 and 0). In order to actualize this between the N-ISDN and the B-ISDN, there are required to provide two devices, i.e., a device for notifying the intrinsic information such as the priority class terminal information etc, and another device for designating the communication priority control in the B-ISDN.
Accordingly, it is a primary object of the present invention, which was devised in view of the above points, to effectively actualize a transmission of the priority information with a simple construction between two kinds of networks having different protocols.